anybody else have this problem?

I never use the self-locking nut in any steering application For two reasons
1) the first one you already know, and
2) the second, because those nuts tend to ef up the threads, either going on or coming off.
lol.
If I am forced to use it;
I use a tap to get rid of the self-locking business, then drill thru the bolt to receive a cotterpin.

When yur done installing it with your home-brew shims to stop vertical movement; the centers of the pivot balls of both the idler and the pitman arm, should, with the chassis levelled front AND rear (not front TO rear), should be approximately the same distance to a level floor. The Idler ball needs to run in the same plane as the pitman ball, as closely as possible.
The holes in the K-member are oversize and
so is the tube in the Idler arm Spacer, and
the slop between the tabs, causing end-play,
are all there to help accommodate this.
Some guys install exact-fit washers, top and bottom and after the alignment, weld those washers to the K. Thus it can't go anywhere, even if something comes loose, or should you need to take the idler down, say to remove the oilpan, to replace a dying rod-bearing.